There have been various electrophotographic technologies for an image forming apparatus. According to one of such technologies, a toner image borne on an image bearing member is transferred onto a belt remaining pinched between the image bearing member and a transfer roller. According to another of such technologies, a belt which constitutes a recording medium bearing member is kept pinched between an image bearing member and a trans fer roller, and a toner image borne on the image bearing member is transferred onto the recording medium on the belt.
In either case, a small gap is present between a transfer roller and a belt, in the adjacencies of the nip, that is, the adjacencies of the contact area, between the transfer roller and belt. This gap is present on both sides of the nip, in terms of the moving direction of the belt (rotational direction of the transfer roller). As transfer bias is applied, a transfer electric field is generated in the adjacencies of the two small gaps. These transfer electric fields are less defined, being therefore likely to cause some of the toner particles, which make up the toner image, to scatter, in particular, on the upstream side of the nip (transfer area). In other words, it is possible that these undefined electric fields will lower the transfer performance of the image forming apparatus. As another type of transferring member which makes contact with the inward surface of the belt, there is a transfer blade. The portion of the transfer blade, which opposes the belt, with the presence of a small gap, is extremely small. Therefore, the electric field, such as the above-described one, which is generated in this area is too small to be one of the causes of the unsatisfactory image transfer. Thus, an image forming apparatus employing a transfer blade is unlikely to suffer from the problem that its transfer performance is reduced by the above-mentioned undefined electric field. However, there is a concern that an image forming apparatus which employs a transfer blade is smaller in transfer area, and therefore, lower in transfer efficiency.
Based on the above-described background, it has been proposed to employ an image transferring member different from a transfer blade in terms of the manner of contact between an image transferring member and a belt. For example, it has been proposed to employ an image transferring member in the form of a rectangular parallelepiped, which is substantially greater, in terms of the area of contact between a transferring member and a belt, than an image transferring member in the form of a blade, which contacts the belt only by its edge and its adjacencies.
However, an image transferring member (which hereinafter will be referred to simply as transferring member) which contacts the belt by the entirety of one of its surfaces is greater, in terms of the frictional resistance between the transferring member and transfer belt, than a transferring member which contacts the belt by its edge portion. Thus, it is possible that as the belt is moved, the transferring member, which contacts the belt by the entirety of one of its surfaces, intermittently separates from, and recontacts with, the belt, with irregular intervals, destabilizing the transfer electric field. In some cases, the transferring member which makes contact with the belt by the entirely of one of its surfaces becomes disengaged from its holder, and/or the transferring member itself tears.